In photovoltaic systems, the low currents produced by the individual photovoltaic cells are combined in parallel in order to provide the current and the total power needed by the utilization system. It is customary therefore that in a photovoltaic system each individual photovoltaic cell is isolated, protected and disconnected. In the field of photovoltaic applications, but more generally in the field of devices for electrical systems, it is known, for this purpose, to use disconnectors and, among these, rotary switches.
Conventional disconnectors are constituted generally by one or more modular contact boxes, each comprising generally a rotatable contact and a pair of fixed contacts. The rotation of the rotatable contact, which in the case of the coupling of two or more modular contact boxes occurs simultaneously for each module, makes it possible to stop or allow the flow of current between the two fixed contacts of each module.
These disconnectors are used both in direct-current circuits and in alternating-current circuits.
A problem shared by all conventional disconnectors, both working in DC circuits and in AC circuits, concerns the need to limit, and possibly prevent, the phenomenon of the forming of what is called the electric arc.
The electric arc is a phenomenon that occurs during the operations for opening and closing an electric circuit. It is produced by the ionization of the air between the electrical contacts, with formation of plasma. In fact, in the opening step, the contact surface between the electrical contacts tends to diminish progressively, with a consequent increase in the current density. As a consequence, the temperature increases to extremely high values, causing the triggering and subsequent development of the electric arc.
The phenomenon of the electric arc is obviously accentuated in the case of DC circuits, because in AC circuits the periodic drop to zero of the electric current value determines a natural and periodic extinguishing of the electric arc.
The formation of the electric arc always entails, however, a deterioration of the contact electrodes and often risks even the welding of the contacts themselves.
Some methods for extinguishing an electric arc are known and implemented in different ways in conventional disconnectors. A first method consists substantially in physically spacing the electrical contacts. A second method consists in inserting further elements of electrical contact, such as metal laminae or magnets, capable of breaking the electric arc formed between the two main contacts, forcing the plasma to expand. A third method consists in increasing the opening speed of the contacts, so as to increase, in the shortest possible time, the physical distance between the electrical contacts.
These disconnectors, however, are not free from drawbacks, including the fact that in order to be able to meet at least partially said requirements they have bulky structures and complex geometries.
Another drawback of these conventional disconnectors is the difficulty in assembling the components.